Dark Matter | SciByte 3

Dark Matter | SciByte 3

This week on SciByte …
We take a look dark matter and dark energy, why even though we can’t see them directly some scientists still believe they exist, where the theories for them came from, what they are, and how they affect the universe.

We’ll also take a look at a few satellites and studies looking for either direct or in-direct evidence of these mysterious phenomenon.

All that and more, on SciBye!

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Show Notes:

Fritz Zwicky  

  • Found a total of 120 supernovae, over a stretch of 52 years.  Involved in using Tpe 1A supernovae as ‘standard’ candles.  In 1937 posited that galaxy clusters could act as gravitational lenses like previously discovered Einstein effect, confirmed in 1979.
  • The first person to provide evidence and infer the presence of dark matter
  • Virial Theorem – for a stable, self-gravitating, spherical distribution of equal mass objects (stars, galaxies, etc), the total kinetic energy of the objects is equal to minus 1/2 times the total gravitational potential energy. In other words, the potential energy must equal the kinetic energy, within a factor of two.

Dark Matter

  • most stars in spiral galaxies orbit at roughly the same speed which suggest that either Newtonian gravity does not apply universally or that, conservatively, upwards of 50% of the mass of galaxies was contained in the relatively dark galactic halo [stars and globular clusters surrounding the galaxy]
  • Astrophysicists predicted the mass would be low in density, but high in temperature (~million degrees Celsius)
  • Theory states there should be about double the amount of matter in the local Universe compared to what is observed
  • the majority of this missing mass should be located in large-scale cosmic structures called filaments – a bit like thick shoelaces
  • Through A Universe Darkly” – A Cosmic Tale of Ancient Ethers, Dark Matter, and the Fate of the Universe

Dark Energy

  • Edwin Hubble first noticed that the Universe was actually expanding, in 1932.
  • Believed to be behind the acceleration of the expansion of the Universe
  • Visual representation of the expansion of the Universe
  • Is Einstein’s vision of gravity, general relativity, incorrect on large cosmological scales?
  • Does “empty space” possess its own energy?

Measuring the Expansion of the Universe [ Hubble constant, or H0 ]

  • Named after Edwin Hubble who first measured the expansion of the universe nearly a century ago
  • Einsteins ‘biggest blunder’ not actually a blunder
  • Type Ia supernovae : produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism
  • Cepheid variable stars are the backbone of the distance ladder because their pulsation periods, which are easily observed, correlate directly with their luminosities
  • Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), two of the nearby satellite galaxies of our own Milky Way Galaxy, since they contain large number of Cepheids, they can be used to calibrate the distance scale
  • Redshift / Blueshift : How fast are things moving away from us? [Red=away]

Cosmic Microwave Background (CMB)

  • Cosmic Background Radiation Image
  • The radiant heat left over from the Big Bang. (first observed in 1965)
  • properties of the radiation contain a wealth of information about physical conditions in the early universe and a great deal of effort has gone into measuring those properties since its discovery.
  • The hot spots and cold spots, which differ in temperature by only millionths of a degree, can be interpreted as very slight differences in the crowding together of matter in the young universe. Hot spots had slightly more matter than average; cold spots a bit less

Wilkinson Microwave Anisotropy Probe

  • 3D model [proposed to NASA in 1995, launched in 2001]
  • cooled microwave radiometers measure the properties of the cosmic microwave background radiation over the full sky
  • Measuring the temperature of the microwave sky to an accuracy of one millionth of a degree revealing conditions as they existed in the early universe
  • using differences in temperature measured from opposite directions (anisotropy).
  • Orbits at Lagrange point 2 :provides for a very stable thermal environment and near 100% observing efficiency since the Sun, Earth, and Moon are always behind the instrument’s field of view


  • property of being directionally dependent
  • defined as a difference, when measured along different axes, in a material’s physical or mechanical properties [light coming through a polarizer]

Wilkinson Microwave Anisotropy Probe results

  • Complete census of the universe finds that dark matter (not made up of atoms) make up 23.3% (to within 1.3%)
  • Accuracy and precision determined that dark energy makes up 72.1% of the universe (to within 1.5%), causing the expansion rate of the universe to speed up.
  • making accurate measurements of the cosmic microwave background fluctuations, WMAP is able to measure the basic parameters of the Big Bang model including the density and composition of the universe
  • Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos.
  • Mapped the Cosmic Microwave Background (CMB) radiation (the oldest light in the universe)
  • WMAP definitively determined the age of the universe to be 13.73 billion years old to within 1% (0.12 billion years)
  • Reported the first direct detection of pre-stellar helium, providing an important test of the big bang prediction. [Jan26, 2010]
  • Nailed down the curvature of space to within 1% of “flat” Euclidean
  • Started to sort through the possibilities of what transpired in the first trillionth of a trillionth of a second, ruling out well-known textbook models for the first time

Australian Student Uncovers the Universe’s Missing Mass

  • Conducted a targeted X-ray search for the hidden matter and within just three months made a very exciting discovery
  • Dark Matter theories have been based solely on numerical models

WiggleZ Dark Energy Survey

  • Einstein Confirmed Again: Dark Energy Present In The Universe
  • Firstly, observed how dark energy opposes gravity by speeding up the overall rate of expansion of the Universe
  • Secondly, observed how dark energy opposes gravity by slowing down the growth of clusters and superclusters with time
  • mapped the distribution of galaxies over an unprecedented volume of the Universe
  • WiggleZ scientists have made a 3-D map of more than 150,000 galaxies near and far to trace the universe’s evolution over time
  • 10min Podcast on WiggleZ

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